The present invention relates to macromers based on methacrylates which correspond to a specific structure that are useful for forming preformed stabilizers which can be used to prepare polymer polyols. In addition, this invention also relates to a process for the preparation of a macromers based on methacrylates that is useful for stabilizing polymer polyols, to novel preformed stabilizers comprising these macromers, to a process for the preparation of these preformed stabilizers comprising these novel macromers, to a process for the preparation of polymer polyols comprising the novel preformed stabilizers, to polymer polyols comprising these novel preformed stabilizers, to a process for the preparation of polymer polyols comprising the ethylenically unsaturated macromers, and to polymer polyols comprises these novel ethylenically unsaturated macromers.
Polymer polyols, also known as filled polyols, are viscous fluids comprising fine particles dispersed in polyols. Examples of solids used include styrene-acrylonitrile co-polymers and polyureas. The solids are typically prepared by in situ polymerization of monomers in the base polyol. Polymer polyols are commonly used for the production of polyurethane foams.
In the present specification, a macromer is defined as a molecule which comprises one or more polymerizable double bonds and one or more hydroxyl-terminated polyether tails. Various macromers are known and have previously been used to stabilize polymer polyols by co-polymerization with one or more ethylenically unsaturated monomers (such as, for example, styrene and acrylonitrile). Because of similarities in chemical composition, the polyether tail(s) energetically favor association with the polyol molecules in the continuous phase rather than with the styrene-acrylonitrile co-polymer. The polyether tails extend into the continuous phase, thereby forming a “brush” layer near the particle-fluid interface which screens the attractive van der Waals forces between particles. This phenomenon is known as steric stabilization. In order to form a brush layer which effectively screens van der Waals forces several conditions must be met. The polyether tails must be similar in chemical composition to the continuous phase so that they fully extend into the continuous phase and do not adsorb to the particles. Also, the surface coverage and molecular weight must be high enough so that the interfacial brush layer is sufficiently thick to prevent agglomeration of the solid particles.
A number of methods for inducing reactive unsaturation into a polyol, thereby forming a macromer, are known in the art. U.S. Pat. No. 6,013,731 teaches several techniques, including reaction of a polyol with unsaturated isocyanates (such as isocyanatoethylmethacrylate (IEM) or α,α-dimethyl metaisopropenyl benzylisocyanate (i.e. TMI)), or reaction of a polyol with maleic acid or maleic anhydride, followed by isomerization of the maleate bond to the more reactive fumarate bond. A macromer prepared by transesterification of a vinylalkoxy silane with a polyol has been disclosed in EP 0,162,589.
The term pre-formed stabilizer is defined as an intermediate obtained by reacting a macromer containing reactive unsaturation (e.g. acrylate, methacrylate, maleate, etc.) with monomers (i.e. acrylonitrile, styrene, methyl methacrylate, etc.), optionally in a diluent or a solvent (i.e. methanol, isopropanol, toluene, ethylbenzene, polyether polyols, etc.) to give a co-polymer (dispersion having e.g. a low solids content (e.g. <20%), or soluble grafts, etc.).
A pre-formed stabilizer (PFS) is particularly useful for preparing a polymer polyol having a lower viscosity at a high solids content. In the pre-formed stabilizer processes, a macromer is reacted with monomers to form a co-polymer composed of macromer and monomers. These co-polymers comprising a macromer and monomers are commonly referred to as pre-formed stabilizers (PFS). Reaction conditions may be controlled such that a portion of the co-polymer precipitates from solution to form a solid. In many applications, a dispersion having a low solids content (e.g., 3 to 15% by weight) is obtained. Preferably, the reaction conditions are controlled such that the particle size is small, thereby enabling the particles to function as “seeds” in the polymer polyol reaction.
For example, U.S. Pat. No. 5,196,476 discloses a pre-formed stabilizer composition prepared by polymerizing a macromer and one or more ethylenically unsaturated monomers in the presence of a free-radical polymerization initiator and a liquid diluent in which the pre-formed stabilizer is essentially insoluble. EP 0,786,480 discloses a process for the preparation of a pre-formed stabilizer by polymerizing, in the presence of a free-radical initiator, from 5 to 40% by weight of one or more ethylenically unsaturated monomers in the presence of a liquid polyol comprising at least 30% by weight (based on the total weight of the polyol) of a coupled polyol which may contain induced unsaturation. These pre-formed stabilizers can be used to prepare polymer polyols which are stable and have a narrow particle size distribution. The coupled polyol is necessary to achieve a small particle size in the pre-formed stabilizer, which preferably ranges from 0.1 to 0.7 micron. U.S. Pat. Nos. 6,013,731 and 5,990,185 also disclose pre-formed stabilizer compositions comprising the reaction product of a polyol, a macromer, at least one ethylenically unsaturated monomer, and a free radical polymerization initiator.
It is known that large, bulky molecules are effective macromers because less material can be used to sterically stabilize the particles. See, for example, EP 0786480. Generally speaking, this is due to the fact that a highly branched polymer has a considerably larger excluded volume than a linear molecule (such as, e.g., a monol), and therefore less of the branched polymer is required. U.S. Pat. No. 5,196,476 discloses that functionalities of 2 and higher, and preferably 3 and higher, are suitable to prepare macromers. EP 0,162,589 and U.S. Pat. No. 5,990,185 describe a macromer, and its use for preparing polymer polyols, wherein the macromer is prepared by transesterification of a vinyl alkoxysilane with a polyol. The preferred macromers comprise the reaction products of vinyltrimethoxy silane, vinyltriethoxy silane, or vinyltripropoxy silane with mixtures of a group of polyether polyols characterized by functionalities ranging from 2 to 6. Such macromers would be expected to have at least 3 polyether tails. Coupling multi-functional polyols with polyisocyanates is also known and described in the field of polymer polyols as a suitable means to increase the molecular weight of the macromer. EP 0786480 discloses a process for preparation of a pre-formed stabilizer wherein the liquid polyol comprises at least 30% coupled polyol. As described therein, a high concentration of coupled polyol is useful for obtaining particles with a small particle size in the pre-formed stabilizer (PFS) and the induction of reactive unsaturation into a coupled polyol is a useful means for incorporating coupled polyol into the particles. U.S. Pat. No. 6,013,731 discloses that the stability of the dispersion can be significantly enhanced by coupling high molecular weight polyols to form an even higher molecular weight product. Macromers prepared from polyols with low intrinsic unsaturation (<0.020 meq/gram) are also described in U.S. Pat. No. 6,013,731. The '731 patent further discloses that such polyols have a low concentration of oxyalkylated, allylic unsaturation-containing monols, and are therefore advantageous because the high concentration of monols present in conventional polyols lowers the average functionality of the polyol.
Macromers based on multi-functional polyols and which have multiple sites of reactive unsaturation are described in U.S. Pat. No. 5,196,476. As described therein, there is an upper limit to the concentration of unsaturation when making macromers by the maleic anhydride route. If the ratio of moles of unsaturation per mole of polyol is too high, then there is a higher probability that species will be formed which have more than one double bond per molecule. Typically, the '476 patent employs from about 0.5 to about 1.5 moles, and preferably from about 0.7 to about 1.1 moles, of the reactive unsaturated compound for each mole of the alkoxylated polyol adduct.
There are also examples in the art of macromers based on “zerols.” As used herein, zerols are polyethers with no terminal primary hydroxyl group. There are a series of patents issued to Dow Chemical relating to the preparation of zerols by derivatizing a polyether monol with an adduct which contains reactive unsaturation. See U.S. Pat. Nos. 4,394,491, 4,477,603, 4,493,908, 4,500,675, 4,663,475, 4,513,124, 4,588,830, and 4,640,935. These patents are similar in that they use semi-batch processes with no pre-formed stabilizer, they focus mainly on acrylate/methacrylate unsaturation, and the end product when monols are used is a zerol with no free hydroxyl group. Key to each patent is the method in which the monol derivatization is performed.
U.S. Pat. No. 5,854,386 discloses stabilizers for polymer polyols which contain both hydroxyl-functionality and unsaturation-functionality. These are prepared by oxyalkylating an unsaturated monomer having at least one oxyalkylatable hydrogen in the presence of an effective amount of a DMC catalyst, and optionally, in the presence of a free-radial polymerization inhibitor. These stabilizers preferably correspond to mixtures containing one or more of the two formulae: R[—(—R2—O—)nH]o or R—(—X—{—(R2—O)n—H}m)o wherein: o is an integer between 1 and 8; n is an integer whose average value is such that the product n·o is from 10 to 500; R2 is alkylene or substituted alkylene; X is a linking group; and R is a C2-30 hydrocarbon containing at least one site of ethylenic or ethylynic (acetylenic) unsaturation, optionally substituted by non-reactive groups and optionally containing interspersed heteroatoms. R may be aliphatic, cycloaliphatic, aromatic, arylaliphatic, heteroaromatic, etc. with the proviso that when R is aromatic or heteroaromatic, the aromatic ring structure is substituted by at least one ethylenic or ethylynic radical-containing group.
U.S. Pat. No. 4,680,358 describes macromers of polyethers having a styryl functional head group on one end, and a terminal hydroxyl group at the other end. These macromers are polymerizable through the head group with a copolymerizable monomer (such as acrylonitrile, styrene, acrylic acid, etc.), and the terminal hydroxyl group at the other end. Polymerization of this macromer yields a polymacromer with a saturated hydrocarbon backbone having polyether branches, i.e. a graft or comb copolymer. These macromers are formed by cationic ring-opening polymerization of a cyclic ether in conjunction with an alkenyl alcohol.
The present invention describes novel macromers comprising one or more ethylenically unsaturated double bond and at least one polyether chain terminated in a hydroxyl group, the preparation of these novel macromers, polymer polyols comprising the novel macromere, and the preparation of these polymer polyols from these novel macromers. The novel macromers of the present invention have at least one double bond and at least one polyether chain with a terminal hydroxy group per molecule. A key advantage of the present invention is ability to produce low viscosity polymer polyols using a variety of macromers based on novel α,β-unsaturated carbonyl compounds.